R ad Rstudio are free software. As such you can easily install them on your computer by first installing R and then Rstudio from Rstudio's official site, without going through Chalmers' APPS framework. Right now, I find Chalmers' APPS a bit clunky and slow to run applications. Therefore I recommend you to strive to install software "the old classic way".

Otherwise (discouraged) you can access both R and Rstudio using Chalmers' APPS , but it is very important that you first read this page or you will be stuck (also here is a useful video if you need extra support). Make sure to keep an eye for possible pop-ups asking you to authorize the execution of software, and also be ready to wait a bit for apps to be launched.

Once both R ad Rstudio are installed, launch Rstudio and this will communicate with R.

You can write in the Rstudio "Console" a simple command like

x<-c(1,2,3)

or you can create a file (script) by clicking the File menu: File-->New-->R script.

Rstudio will communicate with R for doing the actual calculations (so yes, you DO need to install R, as Rstudio is not enough).

Make sure to regularly save your scripts on the cloud (eg on OneDrive) during your session, so not to lose your work.